This invention relates in general to a fuel injector assembly, and more specifically to a fuel injector assembly having a self-locking calibration member that sets spring bias and provides a seat that allows spring alignment.
It is believed that in a conventional fuel injector assembly, a spring is disposed between an end of an adjustment tube and an armature. To allow fuel to flow through the injector, the adjustment tube is usually hollow. It is known to use an adjustment tube to initially set, i.e., calibrate, the dynamic flow of a conventional fuel injector assembly by either altering the amount of metal in the magnetic circuit or by adjusting the spring preload. In the fuel injector industry, adjusting the spring preload is the most common calibration method.
Two types of adjustment tubes are known for adjusting the spring preload: an interference fit adjustment tube and a free sliding adjustment tube. An interference fit adjustment tube requires a large force to position the adjustment tube with respect to its mating part and is considered fixed when the tooling no longer applies the force needed to move the adjustment tube. Interference-type adjustment tubes can be continuous tubes or axially slit tubes, which are commonly referred to as xe2x80x9croll pins.xe2x80x9d A roll pin allows the mating hole size to vary significantly, and moving the roll pin requires less force than moving the continuous tube. However, under severe conditions, the roll pin may be displaced, thus altering the previously calibrated dynamic flow of the fuel injector. The continuous tube is less susceptible to unanticipated displacement due to its higher engagement force, but does require precision machining.
Conventional interference-type adjustment tubes have several disadvantages. One disadvantage is that moving the adjustment tube to calibrate a fuel injector requires a relatively large force. Although moving a roll pin requires less force than moving a continuous tube, a roll pin has the disadvantage of being susceptible to displacement under severe conditions. While a continuous tube is less likely to be displaced than a roll pin because of its higher engagement force, a disadvantage of the continuous pin is that it requires precise machining.
In contrast to interference-type adjustment tubes, a free sliding adjustment tube slides freely with respect to its mating part such that spring preload adjustments can be made quickly. Once the desired spring preload is achieved, the adjustment tube is fixed in position by a staking process with respect to the mating part.
The present invention provides a fuel injector. The fuel injector has a fuel inlet, a fuel outlet, and a fuel passageway extending along an axis between the fuel inlet and the fuel outlet. The fuel injector comprises a body, an armature, a spring, and a spring stop. The body has an inlet portion, an outlet portion, and a passage disposed between the inlet portion and the outlet portion. The armature is disposed within the passage and is displaceable along the axis relative to the body. The spring is disposed within the passage and applies a biasing force to the armature. The spring has a first end disposed proximate the armature and a second end opposite from the first end. The spring stop is disposed within the passage and has a first and second portion. The first portion includes at least one projection engaging the passage. The at least one projection extends obliquely with respect to the axis and in a direction general toward the inlet portion.
The present invention also provides a method of assembling a fuel injector. The fuel injector has a fuel inlet, a fuel outlet, a fuel passageway extending along an axis between the fuel inlet and the fuel outlet. The fuel injector includes an armature and a body that has an inlet portion, an outlet portion, and a passage extending between the inlet portion and the outlet portion. The method comprises disposing within the passage the armature displaceable along the axis relative to the body, disposing within the passage a spring applying a biasing force to the armature, maintaining a seat in a first configuration adapted for applying a first pressure on the passage, positioning the seat in the first configuration at a location along the axis with respect to the body for applying the biasing force, and releasing the seat to a second configuration adapted for applying a second pressure on the passage. The spring has a first end disposed proximate the armature and a second end opposite from the first end. And the second pressure is greater than the first pressure.